Perfluoroaromatic compounds



United States Patent "ice 3,269,928 PERFLUOROAROMATIC COMPOUNDS Robert N. Haszeldine, Disley, and John M. Birchall, Manchester, England, assiguors to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvanra No Drawing. Filed Apr. 5, 1962, Ser. No. 185,221 Claims priority, application Great Britain, Apr. 19, 1961, 14,200/ 61 Claims. (Cl. 204-158) This invention concerns a novel reaction between highly fluorinated aromatic compounds and chlorosilanes to provide novel fluoroaromatic substituted silanes. The invention also concerns'novel derivatives of such fluoroaromatic substituted silanes and improve methods of preparing polyfluoroaromatic compounds.

The reaction of chlorosilanes with fiuoroolefins is known; for example, tetrafluoroethylene reacts with trichlorosilane to form an addition product of the formula SiCl CF CF H. The reaction of chlorosilanes with highly fluorinated aromatic compounds might be expected to follow a similar course resulting in an addition product, but it has been surprisingly found that the reaction follows a completely different course. Instead of an addition product, a substitution product is formed in which a fluorine atom is eliminated from the aromatic ring and a chlorine atom on the silicon atom is replaced by fluorine.

The reaction may be Written as follows:

where Ar is a highly fluorinated aryl radical, R is hydrogen, alkyl, aryl, fluoroalkyl, fiuoroaryl, or fluorine, and n is zero or an integer of 1 or 2. When, in the above formulae, n is 2 the R substituents may be the same or different.

The fiuoroaryl radical Ar will preferably be a pe-rfiuoroaryl radical. Also included in this invention are fiuoroheterocyclic radicals having aromatic characteristics. The preferred Ar radicals are perfluoroaryl radicals such as perfluorophenyl and perfluoronaphthyl radicals. The Ar radicals may be substituted with alkyl or perfluoroalkyl groups; e.g., methyl, perfluoromethyl, ethyl, isopropyl, n-butyl, t-butyl, perfluoroethyl, etc. Thus, examples of specific p'erfluoroaryl radicals will include perfiuorophenyl, perfluorotolyl, perfluoronaphthyl, perfloro(methylnaphthyl), perliuoroxylyl, perfiuoro(ethylphenyl), 2,3,4,5- tetrafluorotolyl, 2,3,5,6-tetrafluorotolyl, 2,3,4,5,6,7-hexafluoronaphthyl, 2,3,4-,S-tetrafluorophenylethyl, 2,3,5-trifiuoro-4-methylpyridyl, and the like. In general the fiuoroaryl radical will be any of the defined fluorinated aryl radicals which contain from 6 to 12 carbon atoms. The R radicals defined above will preferably be hydrogen, fluorine, lower alkyl and fluoroalkyl radicals ('e.g. methyl, ethyl, propyl, butyl) perfluoromethyl, etc. and aryl and fiuoroaryl radicals containing six to ten carbon atoms (e.g. phenyl, perfluorophenyl, perfluorotolyl, ethylphenyl, naphthyl, etc.).

More specifically, when the reactants are hexafiuorobenzene and trichlorosilane the reaction is as follows:

3,269,928 Patented August 30, 1966 The surprising features of the reaction are (a) that it is the first reported instance of free radical attack upon a highly fluorinated aromatic system to give an aromatic product and (b) that in the course of the reaction a fluorine atom migrates from the aromatic nucleus to the silicon atom.

The reaction is favored by conditions conducive to the formation of free radicals, particularly irradiation by ultraviolet light and/ or heat. Chemical initiators may be used as well as or instead of such external activation energy sources. The chemical initiators used may be of any of those usually used in initiating free radical reactions including organic peroxides such as benzoyl peroxide and azo-compounds such as dimethyl-azo-diisobutyrate. When using actinic radiation as the initiating agent heat is not essential and the reaction may be conveniently conducted at room temperature or lower. With chemical initiators, however, heat will usually be required and temperatures of from 50 to 500 C. are found satisfactory.

As indicated by the formula given, the product of the reaction is mainly a mono-substituted aromatic compound. This is particularly so when a molar excess of the fluoroaromatic compound is used. However, when substantially equimolar quantities, or a major excess of the silane are used, some higher substitution products are obtained, e.g.

CH3 F F F/\N F F F F FM )F vF F F OFa N/ N/ N/ and the like. Particularly preferred perfluoroaromatic compounds are those of the formula C6F (Rf)6 where Rf is perfluoroalkyl and m is an integer of from 1-6.

The preferred mono-substituted products of the invention form a new class of aromatic substituted silanes of the formula Ar SiFCl R where Ar R, and n are as defined above. Particularly preferred products are those of the formula Ar SiRFX where R is hydrogen, alkyl, aryl, fiuoroalkyl or fiuoroaryl, and X is chlorine or fiuorine, the alkyl, aryl, fluoroalkyl and fiuoroaryl radicals containing from one to ten carbon atoms. The silane products of this latter formula are readily hydrolyzable by water to form a series of novel silicones and polysiloxanes which are stable thermally and particularly stable to water and acids. In strong aqueous alkali further hydrolysis of the silicones and .polysi-loxanes takes place in the course of which the silicon atom on the perfluoroaromatic nucleus is replaced by hydrogen. This is a particularly useful reaction since once a hydrogen is introduced into a perfluoroaromatic system it provides a point for further chemical attack thereby enabling conversion into other useful chemicals.

The novel silicones which may be prepared according to this invention from the mono-substituted derivatives are of the general formula (Ar SiR'O) Where Ar and R are as previously defined and z is an integer. They may be prepared by reacting the fluoroaromatic compound with a silane of the formula RSiHClX followed by hydrolysis of the silane formed with water, e.g.

U.V. light H1O CsFe-i-RSlHClX camsiR'FX (CB fiSlR'O)! Where the starting silane is dichlorosilane there arises the possibility of a two stage reaction with the fluoroaromatic compound, for example:

U.V. light H2O C(iFs SiHCls C'sFsSiFClz (csFssiom) I Where hydrolysis is carried out on a silane of structure Ar SiR F where R is alkyl, aryl, fluoroalkyl or fluoroaryl, the products obtained are disiloxanes, viz:

As stated above the novel silicones and polysiloxanes are highly stable except to strong alkali in which they are further hydrolyzed, for example:

NaOH aq. (CsFssiom) z CnFgH There is of course no need to proceed via a silicone or polysiloxane to obtain the hydrogen containing perfluoroaromatic derivative, since the silane products, including those containing only one halogen atom attached to the silicon atom, may be hydrolyzed directly by strong alkali, e.g.

NaOH aq. CaF5SiFC12 CaFrH It will be seen therefore that the invention provides a route to monohydro-perfiuoroaromatic compounds which is especially useful for preparing compounds of the type C F H(R where m is 1-6. Particularly the invention provides a new route to pentafluorobenzene and the best method yet produced for the conversion of hexafiuorobeuzene into pentafluorobenzene. From pentafluorobenzene and othr monohydro-perfluoroaromatic compounds other useful intermediates may be prepared such as CGF5I and C6F5BI'.

The higher substituted silane products, which may, as indicated, be obtained by the reaction of the perfluoroaromatic compound with an equimolar or a molar excess of the silane, with or without the separation of a lower substituted intermediate, are also subject to hydrolysis in a similar manner to the mono-substituted products. Of particular note are the polyhydroperfluoroaromatic compounds which are formed by hydrolysis in strong aqueous alkali, e.g.

Besides being useful intermediates, the thermal and chemical stability under neutral and acid conditions of the silicones and siloxanes renders them useful as lubricant oils and greases and resins.

The invention is illustrated by the following examples:

EXAMPLE 1 (a) Preparation of (pentafluorophenyl)dichlorofluorosilane Dry hexafluorobenzene (10.0 g., 0.054 mole) and freshly distilled trichlorosilane (8.0 g., 0.059 mole) were sealed into a 350 ml. silica tube and irradiated by a 500 watt mercury discharge tube for 250 hours. The reaction tube was shaken vigorously throughout this period. At the end of the irradiation, the tube was cooled to C., and volatile products (790 ml. at N.T.P.; M.W. 38.9) were transferred to a high-vacuum apparatus and identified by infrared spectroscopy as hydrogen chloride containing traces of silicon tetrafluoride. The liquid reaction products wer transferred and distilled under dry nitrogen and yielded fractions boiling 80148 C. (1.8 g.) and 148-170 C. (6.2 g.). The latter fraction was redistilled under reduced pressure and gave (pentafluorophenyl) dichlorofluorosilane (5.0 g.). (Found: C, 25.2, CI, 25.1, F, 38.9%. C C1 F Si requires: C, 25.3, CI, 24.9, F, 40.0%), B.P. 54 C./13 mm. Gas-liquid chromatographic analysis of the remaining fractions from the distillations showed that some hexafluorobenzene (2.2 g., 22%) remained unreacted, and analysis of the siliconcontaining fractions by hydrolysis showed that the total yield of (pentafluorophenyl) dichlorofluorosilane was at least 7.2 g. (60% based on hexafluorobenzene transformed).

(b) Hydrolysis of (pentafluorophenyl)dichlorofluorosilane Water (25 ml.) was added in five portions to (pentafluorophenyl)dichlorofluorosilane (24.0 g.) contained in a partially evacuated 2.5 liter bulb; a vigorous reaction occurred at each addition and a white polysiloxane was formed. Aqueous sodium hydroxide (40%; ml.) was then added slowly and the reaction was completed by heating on a steam bath for 15 minutes. The volatile contents of the bulb were transferred to a high-vacuum apparatus, dried with phosphorus pentoxide, and identified as pentafluorobenzene (10.0 g., 71%) by elemental analysis and molecular weight measurement. (Found: C, 42.8%; H, 0.9%; M, 168. Calc. for C HF C, 42.8; H, 0.6%, M, 168.) The purity of this product was confirmed by gas-liquid chromatography.

EXAMPLE 2 Reaction of 2,3,4,5,6-pentafluarotoluene with trichlorosilane 2,3,4,5,6-pentafiuorotoluene (18.4 g., 0.10 mole) and trichlorosilane (14.8 g., 0.11 mole), in a 350 ml. sealed silica tube, were irradiated by a 500 watt mercury discharge lamp for 192 hours. The gaseous products (1331 ml. at N.T.P. Found: M 44) were shown by infrared spectroscopy to consist of hydrogen chloride, silicon tetrafluoride, and a trace of carbon dioxide. The liquid products were distilled and gave 2,3,4,5,6-pentafluorotoluene (9 g.), B.P. 116-120 C., and a fraction B.P. 92-99 C./ 37 mm. (7 g.). The latter was redistilled to give a liquid (5.6 g., 39% based on pentafiuorotoluene converted), B.P. 98-99 C./37 mm., which was shown to consist of a mixture of isomeric (methyltetrafluorophenyl) dichlorofiuorosilanes by elemental analysis. (Found: C, 29.8, H.

C H Cl F Si requires: C, 29.8, H, 1.1%) and gas- By following the procedural details given in the above examples, the following reactions may be carried out to obtain the products indicated:

Ar: SiHC K-n n Product r F F --SiFC1CHs SiH 0120B;

F F F F and meta and para isomers F F F F F F F Si FzCl SiH C12 F F F F F F F F F and alpha isomer F F F F SiH Clg F F I -Si FH Cl and meta and para isomers (I) F F3 F F F -Si F C1CsH5 SiHClaC H5 C Fr- F O F: F

and isomers F F F -Si F ClCoHg SiH 011C 0H5 F F F F C F; C Fr 0 F3 I I I F F F -Si F SiHgCli I F F F F F F F F F F Si F CH3) 1 SiHCKCHa):

I F F F F F F F F SiHC1(CHs)2 F SiF(CHs):

F F F F F N F N and isomers F N SiH ClzF N F F F F SiFzCl and isomers An SiHCh-DRn Product 0 F; C F; 5

F F F -SiFH o1 SiHgCli F F F F C Ha C H:

and isomers (fHzCHrCHz (EHzCHzCHa F F SiH 01:0 6II5 F SiF 010 @Hi F F F F and isomers SiF OH F F F I a) HsC- F SiHCl(CHs)2 F -CH:

F F F F F F F F and isomers Likewise when the caustic hydrolysis step of Example 1 is carried out, products are obtained as follows:

If instead of using strong alkaline hydrolysis, simple aqueous hydrolysis is employed, silicones and siloxanes may be obtained as follows:

Compound hydrolyzed: Product obtained G 5 Z 2 6 5)2 ]z (CR-C 1 SiF (CF C F SiO] Z (CF C F SiFCl (CF C F SiO 1 5 z It will be obvious to the skilled art worker that numerous changes and variations may be made from the above description of the invention and the examples without departing from its spirit and scope.

We claim:

1. The process of preparing a fluorinated aryl substituted fluorosilane which comprises reacting in the presence of a free radical initiator, a highly fluorinated aromatic compound containing 6 to 12 carbon atoms and containing at least 4 fluorine atoms attached to the nucleus of the aromatic ring with a silane having the structure SiHC1 R where R is a member of the group consisting of hydrogen, fluorine, alkyl, aryl, fluoroalkyl and fluoroaryl radicals and n is a number from 0 to 2.

2. The process of preparing a perfluoroaromatic substituted fiuorosilane which comprises reacting a perfiuoroaromatic compound with a silane having the structure SiHCl R where R is a member of the group consisting of hydrogen, fluorine, alkyl, aryl, fluoroalkyl and fluoroaryl radicals and n is a number from 0 to 2, said reaction occurring in the presence of a free radical initiator,

3. The process of preparing (methyltetrafluorophenyl) dichlorofiuorosilane which comprises reacting 2,3,4,5, 6-pentafiuorotoluene with trichlorosilane in the presence of a free radical initiator.

4. The process of preparing (pentafiuorophenyl)dichlorofiuorosilane which comprises reacting hexafiuorobenzene and trichlorosilane in the presence of a free radical initiator.

5. The process of claim 4 wherein the free radical initiator is ultraviolet light.

8 Refereuces'Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 12/ 1956 Canada. 2/ 1960 France. 4/1954 Great Britain.

TOBIAS, E. LEVOW, Primary Examiner.

SAMUEL H. BLECH, Examiner.

20 I. G. LEPITI, Assistant Examiner. 

1. THE PROCESS OF PREPARING A FLUORINATED ARYL SUBSTITUTED FLUOROSILANE WHICH COMPRISES REACTING IN THE PRESENCE OF A FREE RADICAL INITIATOR, A HIGHLY FLUORINATED AROMATIC COMPOUND CONTAINING 6 TO 12 CARBON ATOMS AND CONTAINING AT LEAST 4 FLURINE ATOMS ATTACHED TO THE NUCLEUS OF THE AROMATIC RING WITH A SILANE HAVING THE STRUCCLEUS OF THE AROMATIC RING WITH A SILANE HAVING THE STRUCSISTING OF HYDROGEN, FLUORINE, ALKYL ARYL, FLUOROALKYL AND FLUOROARYL RADICALS AND N IS A NUMBER FROM 0 TO
 2. 